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PSU fails after 3 months

Hi, I'm troubleshooting a friend's computer, with Pentium 4 2.4GHz, 256MB RAM, 40GB HDD, 1 CD-RW, 1 CD-ROM. The monitor is not connected to the PSU, but straight to the Mains power supply. The computer is protected by an Automatic Voltage Regulator (so less chance of the damage caused by electrical shocks I suppose). The current PSU's power rating(which has failed) is 450W.

The LED on the motherboard (Asus) lights when the Mains is switched on. But pressing the power button has no effect whatsoever, nothing starts, nothing turns (including the PSU's own fan).

Changing the PSU solves the problem. I've checked, and found nothing physical which I suspect will cause any short circuits.

With the load, 450W should be okay right? Or is this the issue here?

Do you think it's just bad luck that by chance, his PSU is damaged after 3 months, or should I suspect something else is not going well in the computer?

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Any number of issues.

In reply to: PSU fails after 3 months

From just bad luck, bad capacitors to a box that is hot to the touch.

450 usually is fine, but there can be a reason if it happens again. Look out for a common issue. Type in BAD MOTHERBOARD CAPACITORS at google.com to get the picture.


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About the bad PSU

In reply to: Any number of issues.

Thanks everyone for your responses.

Bob, just curious: if the (faulty) PSU when connected to the motherboard, does cause the LED on the motherboard to light, but pressing the On button has no effect (of starting the system, even when all the Molex connectors to the HDD, and all other devices are disconnected), is it the circuity in the PSU itself is faulty, or should I suspect the Motherboard Connector from the PSU (ATX1 I suppose?) that is faulty?

Of course I'm not going to great lengths of 'repairing' the PSU (I don't have the expertise and I know the associated risks of doing that), but just like to know on an 'academic' knowledge basis.

Thank you.

P/S: If the motherboard connector is not called ATX1, please enlighten me on this. Thanks.

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In short.

In reply to: About the bad PSU

The LED may require one of the 3 supply legs to function.

Did you check it out with a voltmeter?

Also, the rise time of the power supply may not be met. To check this out, you need an oscilloscope. Did you look at this?


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Haha.... alright

In reply to: In short.

Hi Bob. Looks like it's impossible for me to determine it then... Don't have the tools and expertise required. Anyway, thanks for your help!

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This is why...

In reply to: Haha.... alright

Replacements are the right way to do this AFTER you do the visual inspection for BULGING or LEAKING CAPACITORS. Those BAD MOTHERBOARD CAPACITORS are still showing up and one of the symptoms is the blown PSU.

Give we can find 450 and more Watt PSUs for less than a good voltmeter, it is an accepted repair method.


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Most likely, the light that you

In reply to: About the bad PSU

are speaking of is the one that most mobo's now have on them. It shows that the 5 volt standby power is applied to the mobo. That power [very low power capability] is what is used by the built-in logic on the mobo that turns the high power outputs [rails] on when one pushes the power on button [or wake on LAN, or any other Wake on functions]. Since the new supply worked, the problem is not in the logic circuit, the switching or one or more rails inside the supply has/have failed.

The 5 volt standby is on pin 9 of both the 20 pin and 24 pin just in case you want to check. You can do this on the bench with the supply simply plugged into an outlet. You can also try to start the supply by jumpering the green wire to any of the black wires. [pin 14 in a 20 pin connector pin16 in the 24 pin]. Of academic interest only.

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Power supplies, like any other

In reply to: PSU fails after 3 months

electrical device can fail due to a random failure of a component.

That load for a legitimate 450 watt power supply is not too high, but there are some low grade supplies around.

As they say for infant mortality failures, if they run for a few months they go for years. But infant mortality failures do occur. Mfr's do burn in at their factory to attempt to have them occur before delivery, but some do get through.

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Under the hood...

In reply to: PSU fails after 3 months

I taken some p/s's apart and usually found three problems with them. The caps have blown or failed, fault ckt. gone or stressed(delamed) solder runs. Ironically, fuses rarely blow, until the failure is really apparent. replace the fuse, it blows again. Cheap p/s units use cheap componets or under-rated ones. The best bet w/o opening a p/s is to feel the weight if it "heavy" its using bigger caps, maybe fatter guage wiring and/or big heat sink. I remember when older XT power supply were 3X the weight of a newer ATX one and they only put out 55-75W of power, go figure. The lesson here is to buy a high wattage unit and a namebrand and pay alittle more for it.

tada -----Willy Happy

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and stable, good rails

In reply to: Under the hood...

you want enough Amperage, and stable voltage
and the heavy thing is a very quick way to test any amiplifcation/power adjusting equipement

if you've ever seen Jurassic Park
when the kid finds the nightvision
and the lawyer says "Are they heavy?"
the kid "yea"
the lawyer "then put them down, their expensive"

it's usually the rule with this kind of equipment too
high grade home audio amps that kick out 3000W or more, weigh over 100 lbs easily (why do you think they go on the bottom shelf/floor?)

a good PSU should be heavy, and a cheap PSU is usually lighter than a full soda can

i'd suggest a few brands such as Antec, Enermax, Fortron Source, Sparkle Power, OCZ, PC Power & Cooling (often shortened to PCP&C), and Zippy/EMACS

just check www.newegg.com
or if you want a PCP&C unit

they are often considered to be the best PSU's on earth

Thermaltake's PSU's are decent for the money, but their not great (they are between the crap, and the above mentioned brands' good products (they are about a step above middle of the road)

Thermaltake's PSU's aren't low grade
but their issue is usually rail sag (the 12v sometimes sags to like 11.7, which is way to low)

but Thermaltake's units have interally adjustable rails (you have to open the casing, and know what to adjust, but it's simple (just look on google)) and you can raise the rails up to a more stable level

and the Thermaltake's only sag if you load them heavily
if your running a basic system on a Thermaltake, it's a fine buy for the money (their $60 480W unit is what i'm talking about here, i'd ignore all their other units (their $230+ one is ignored because i'm guessing you don't want to spend that much)

in general i'd have no issues with a Thermaltake PSU
but i'd take any of the above brands over a Thermaltake

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Gee, I remember when the magnet weight of a speaker

In reply to: and stable, good rails

for a way to evaluate for super bass response. Then the crooked outputs loaded the speaker with a load of pot metal, with zero magnetic properties.

The weight of well designed heat sink is fine. The cheapies will still add some crap if weight becomes the criteria.

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Hey old timer..

In reply to: Gee, I remember when the magnet weight of a speaker

I replaced my 300 watt supply with a 450 watt not long ago, and the new supply was much lighter in weight, even though it had an additional fan.
Not sure "weight" is the right thing to use when judging quality, as new designs in heatsinks, and thermal compounds, may be changing the "hefty, heavy" thing about durability.
Not a total convert though, as we still like to cook in cast iron pans. LOL.

Younger Ray

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